Isolation of nontransforming mutants of Polyoma virus on normal cells to test the indirect mode of action of the NG-18 gene (producing its effect via the cell genome) using 3T3 cells (nonpermissive host) and BMK cells (permissive host). Test for alteration of cellular functions such as DNA synthesis, cell surface alteration, RNA synthesis, elevation of thymidine kinase, and other enzymes related to DNA synthesis in permissive and nonpermissive cells by NG-18 polyoma virus. Definition of permissive factors in transformation by polyoma mutant NG-18 with normal (nonpermissive) and leukemia virus infected (permissive) cells derived from mouse, rat, and hamster embryos.